This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Inhibitors of apoptosis (IAPs) are multi-domain anti-apoptotic factors that can block cell death. IAP family members contain a C-terminal RING domain with E3 ubiquitin ligase activity. Binding of small molecule antagonists to IAP repeats within cellular IAPs (cIAPs) promotes cIAP auto- ubiquitination and proteasomal degradation, thereby releasing cIAP inhibition of apoptosis. Small molecule binding remote from the RING domain induces ligase activity, and a conformational change we want to understand. We seek SAXS data from cIAP1 both in the absence and presence of small molecule antagonists.